I'm trying to add some silnyl pockets to my big ultrasil daypack without sewing, but nothing I have seems to stick. The pockets won't have much stress on them and I'm concerned about creating potential leaks if I sew them on. I've tried professional contact cement, rubber cement, and superglue gel, but the pockets just slide right off. Is there an adhesive that will make a permanent bond between ultrasil and silnyl? Thanks.

Dilute some silicone caulk w/ mineral spirits (mix until syrup-like). Then apply it where needed and put (clamp if necessary) the two pieces of fabric together for a few hours. Allow to cure overnight in a dry place.

Unfortunatly, silicone is not real sticky to much once it dries. Trying to glue on pockets is also an almost sure to fail. The direction of stress is away from the glue line, not across it, even if you were successfull. Over a few uses, it will still come loose using an adhesive silicone. I would suggest you have to sew it, then seal the stitching.

I agree with James. The bond will be "in peel" and I think you'll be disappointed with the durability. Silicone adhesives are the only type that will bond those surfaces, and silicone adhesives are not known for high strength. The pocket will eventually peel off. The only way to do this, as far as I know, is to sew first and then seal the seams with silicone sealant.

Do not agree as to dilutions, slurries and what-have-you. The don't hold.

The best I've found is GE silicone glue (NOT THE SEALANT). It works well for reinforcement patches on flies, but I would not ever trust it to hold a pocket on a pack, or a structural seam on a tarp or fly. Sew and seal = 1+.

For more info, search BPL for the article on bonding silnylon that was republished about a year ago. The author still occasionally posts on BPL, and I got the tip about the glue/sealant distinction from one of his posts. It greatly improved the bond on my patches, and eliminated a lot of sewing.

The glue is not found in most hardware stores, but is cheap on the web.

if it has to be glued on i would trust nothing but 3m 9460vhb tape. with a primer to clean the contact area first. i have seen both in at least one cuben supplyers site. sorry but i can't remember which one that was- but they were selling the tape per foot.

I have to disagree about the tape. 3m's 9460 VHB transfer tape forms a very strong bond (for tape) on metals and other relatively high-energy surfaces, but it won't work on the silicone surface of silnylon for the same reasons that it wouldn't work on PTFE, PFA, polyethylene, or polypropylene.

Tapes, in general, don't achieve the bond strengths of liquid adhesives, and this tape is no exception. It is used in industrial assembly applications for the same reasons that anyone uses tape: it is fast and clean. This is the same reason that tapes are used for cuben gear (and cuben sails).

If you need to glue, a silicone adhesive is the only thing that will bond to silnylon, and silicone adhesives have low strength compared to urethanes, acrylates, and other classes of adhesives.

I was told that my folded and glued ridgeline seam would peel (fail) with little stress. Well, I've had it on one trip per month since August with no failure and I'll let you know how it fairs on a 5 day trip in Jan and a 9 Day trip in Feb under a snow load.

> If you need to glue, a silicone adhesive is the only thing that will bond to silnylon,
> and silicone adhesives have low strength
More or less correct. To bond to silicone polymer you need a siloxane adhesive. Silicone adhesive is a member of this class.

But there are also hard-to-get esoteric siloxane transfer tapes and single-sided and double sided tapes which can bond. A few of them are high-strength – quite good in fact. Yes, I have used them on my silnylon tents, for the last 5 – 10 years.

But note two things: such adhesives take >72 hours to fully bond: it is actually a genuine chemical reaction between the adhesive and the cured polymer in the fabric. And at present they are quite expensive.

In general I agree with the sew-then-seal approach. I would add that it helps to reinforce the back surface first. Using a silicone adhesive over a large area is also good.